Because it only takes a few votes to get on the front page, David has some HN readers that subscribe to his blog, so within a few hours of submitting, 1-2 upvotes put it on the front page. Once it's there, more people see it and upvote it. It doesn't take much.

On a depressing note, once an author has a history of getting upvoted (37s, Godin, Maroon), people race to submit anything they write so they can get karma.